2.A.1.2.57
MFS-type polyamine transporter SLC18B1 or VPAT (Solute carrier family 18 member B1) of 456 aas and 12 TMSs.  Polyamines synthesized in neurons and astrocytes are stored in secretory vesicles and released upon depolarization. Vesicular storage is mediated in an ATP-dependent, reserpine-sensitive process.  SLC18B1 is the fourth member of the SLC18 transporter family, which includes vesicular monoamine transporters and a vesicular acetylcholine transporter. Proteoliposomes containing purified human SLC18B1 protein actively transport spermine and spermidine in exchange of H⁺. The SLC18B1 protein is predominantly expressed in the hippocampus and is associated with vesicles in astrocytes. SLC18B1 gene knockdown decreased both the amount of the SLC18B1 protein and the spermine/spermidine contents of astrocytes (Hiasa et al. 2014).  Slc18b1 knock out mice have reduced polyamine content in the brain These mice have impaired short and long term memory in novel object recognition, radial arm maze and self-administration paradigms (Fredriksson et al. 2019). Moreover, Slc18b1 KO mice have altered expression of genes involved in Long Term Potentiation, plasticity, calcium signalling and synaptic functions, and expression of components of GABA and glutamate signalling are alterred. These mutants show partial resistance to diazepam, manifested as lowered reduction in locomotion after diazepam treatment. Possibly, removal of Slc18b1 leads to reduction of polyamine contents in neurons, resulting in reduced GABA signalling due to a long-term reduction in glutamatergic signalling (Fredriksson et al. 2019).